[Tutor] Mount size

[Danny Yoo]

On Wed, 27 Oct 2004, Faulconer, Steven M. wrote:


> We are having some issues getting reliable information for available disk
> space within Python programs. We are using os.statvfs to get the blocks
> free, but the numbers are not consistent between local and NFS mounted
> drives.

[some text cut]

> Given that f_bavail is the number of blocks available (non-superuser) I
> would assume that we could multiply that by f_bsize and then divide by 1
> million (for megabytes) or 1 billion (gigabytes).


Hi Steven,



You may want to use f_frsize, not f_bsize.  The underlying man page for
statvfs says the following about the tuple that we get back:

"""
     u_long      f_bsize;             /* preferred file system block
                                         size */
     u_long      f_frsize;            /* fundamental filesystem block
                                         (size if supported) */
     fsblkcnt_t  f_blocks;            /* total # of blocks on file system
                                         in units of f_frsize */
     fsblkcnt_t  f_bfree;             /* total # of free blocks */
     fsblkcnt_t  f_bavail;            /* # of free blocks avail to
                                         non-super-user */
     fsfilcnt_t  f_files;             /* total # of file nodes (inodes) */
     fsfilcnt_t  f_ffree;             /* total # of free file nodes */
     fsfilcnt_t  f_favail;            /* # of inodes avail to
                                         non-super-user*/
     u_long      f_fsid;              /* file system id (dev for now) */
     char        f_basetype[FSTYPSZ]; /* target fs type name,
                                       null-terminated */
     u_long      f_flag;              /* bit mask of flags */
     u_long      f_namemax;           /* maximum file name length */
     char        f_fstr[32];          /* file system specific string */
     u_long      f_filler[16];        /* reserved for future expansion */

"""

(Taken from Solaris 8 man page on statvfs)


The way that the docs make a distinction between the "preferred" and
"fundamental" block sizes is significant.  Use 'f_frsize' instead, and
you should get better results.



There's also a section in the BUGS that says:

"""
BUGS
     The values returned for f_files, f_ffree, and  f_favail  may
     not be valid for NFS mounted file systems.
"""

So be careful not to depends on those particular values on NFS-mounted
drives.



I hope this helps!